Alkali free alumino-silicate glasses, such as, glasses for Liquid Crystal Display (LCD) substrates using amorphous silicon or oxide thin film transistors (TFTs), or glasses for organic light emitting diode (OLED) substrates using low temperature polysilicon (LTPS) TFT deposition have been designed to allow high temperature processing (up to 700° C.) while not suffering from deformation. These glasses can be formed using a fusion draw process where liquid glass flows over the lips of a glass overflow forming block made of zircon (ZrSiO4) material and fuses at the bottom of the glass overflow forming block to form a sheet. Zircon forming blocks that come in contact with alkali free alumino-boro-silicate glasses offer good corrosion resistance and mechanical properties at the forming temperature of glass. However, it has been observed that bubble inclusions may occur in the glass formed using zircon forming blocks. Bubble inclusions in the glass are not acceptable for the TFT substrate application.